The present invention relates to the field of imaging laser sensitive media using lasers. Specifically, the invention relates to a technique of debris removal for an ablative imaging process.
The notion of using laser imaging is well known in the art. A laser sensitive media is mounted onto the surface of an imaging cylinder and an image is imparted onto the media using a focused write laser of relatively high power. This process is known as xe2x80x9cimagingxe2x80x9d and the laser sensitive media bearing the image is said to be xe2x80x9cimagedxe2x80x9d.
During imaging, the interaction of the laser and the media causes a physical and/or chemical change to the imaged areas of the media. In the process of imaging, matter may be expelled from the laser sensitive media. The expulsion of matter from the media is referred to as ablation. The matter expelled may consist of solids, liquids, gases and plasma; which is commonly considered to be smoke or particulate debris. This smoke and particulate debris are referred to in this application as xe2x80x9cablation byproductsxe2x80x9d, xe2x80x9cablation dustxe2x80x9d or xe2x80x9cablation debrisxe2x80x9d.
Ablation byproducts present several difficulties, which may hamper the imaging process. A first problem is related to the immediate effect of the smoke and particulate debris, which accumulates in the imaging area. The functionality of the imaging lasers is impeded by the ablation byproducts in the vicinity of the imaging area. If the lasers are obstructed by smoke and particulate matter, then the result will be a poorly imaged laser sensitive media. Consequently, a need exists for a technique to remove the ablation byproducts from the imaging area in a manner that prevents any negative interaction between the ablation byproducts and the lasers.
When created during the imagewise ablation of a laser sensitive media, the ablation byproducts can also resettle onto the media; this is known as redeposit. This is a particularly critical problem in imaging laser sensitive media, because redeposit can be associated with imaging artifacts which are visible on the final product. Once redeposit has occurred it is difficult to remove the ablative byproducts from the media. Consequently, debris that has resettled onto the media is difficult to remove without damaging the image. A need exists for a technique to remove ablation byproducts from the imaging area of a laser sensitive media so as to minimize the amount of redeposit of debris on the surface of the laser sensitive media.
A third problem associated with ablation byproducts is related to the tendency of the ablation debris to accumulate in the sensitive areas of the imaging lasers and other areas of the imaging device. The ablation debris is dust-like in nature and has a tendency to accumulate almost anywhere. Accumulation of ablation debris can cause severe degradation and/or damage to the components in the imaging system, particularly the laser optics. For example, if a layer of debris collects on a lens, it may drastically affect the lens"" optical performance. For this reason, a need exists for a technique of removing ablation byproducts completely and efficiently from the vicinity of the imaging lasers and the other sensitive areas of the imaging device.
The nature of the ablation byproducts presents a difficulty with respect to its movement. Any attempt to physically move ablation byproducts in a rapid manner is likely to create a dispersing and fast moving plume of ablative byproducts. Once a plume of debris is created in this manner, it may become exceptionally difficult to control or direct and efficiently collect or remove from the imaging device. As a result, a need exists for a technique to direct and trap ablative debris away from the vicinity of an imaging area in a controlled manner, so as to allow efficient collection or removal of the debris.
FIG. 1 depicts two of the techniques used in the prior art. Laser 11 in the imaging head 10 is focused on the imaging area 14 of the media 15 by the laser optics 12 and 13. To date, debris removal techniques have concentrated on sucking or blowing the debris out of the imaging area 14. When ablation byproducts (not shown) are created, they may be sucked out of the imaging area 14 by vacuum source 17. Alternatively, the ablation byproducts may be blown out of the imaging area 14 by air jet 16. Each of these prior art techniques suffer from some of the aforementioned drawbacks. Specifically, the vacuum source 17 does not remove the ablation byproducts very effectively and there may be substantial interference with the lasers. In addition, the method involving air jet 16 effectively removes the debris from the imaging area 14, but generally causes the dispersion of the dust, allowing it to settle on the functional elements of the imaging head 10, and back onto the laser sensitive media 15.
In accordance with the present invention, a method and apparatus for the removal of byproducts associated with laser ablation on a laser sensitive media is disclosed. The invention involves a principal source of fluid flow (a component of which is oriented in a principal direction) and a secondary source of fluid flow (a component of which is oriented in a secondary direction). The principal and secondary sources of fluid flow are then used to direct the ablation byproducts. The ablation byproducts are moved in the principal direction and away from the vicinity of the imaging area by the principal fluid source. However, the debris is simultaneously restrained, so as to ensure that it does not travel too far in the principal direction and that it is not excessively dispersed. The invention also involves a sink, to which fluid moves, which collects the ablation byproducts and removes them from the vicinity of the imaging area.
A laser is given in this application to be any electromagnetic radiation of enough intensity to cause ablation as defined above.
Advantageously, the principal and secondary sources of fluid flow may be effected by a plurality of fluid sources.
Preferably, the sources of fluid flow may be effected by orifices attached to sources of pressurized fluid.
Advantageously, the sink, to which fluid moves, may be effected by a plurality of fluid sinks.
Preferably, the sink may be effected by an orifice attached to a vacuum source.
The laser sensitive media used in the present invention may be mounted on or integral with a flat surface, cylindrical surface, or other advantageous geometry.
Advantageously, the laser sensitive media may be usable in a printing process, which is one of: flexographic printing, lithographic printing, letterpress printing, gravure printing, or xerographic printing.
Advantageously, the invention may involve the additional provision of a barrier adjacent to the imaging area. The barrier is operative to allow the ablation byproducts to pass by the barrier in the principal direction, but to help bias the flow of fluid in the secondary direction.
Another aspect of the present invention concerns a method and apparatus for the removal of the byproducts associated with laser ablation on a laser sensitive media. As before, this aspect of the invention involves providing a principal source of fluid flow. The principal source of fluid flow (a component of which is oriented in a principal direction) directs the ablation byproducts away from the imaging area in the principal direction. A counter-flow source of fluid flow is also required. The counter-flow fluid source creates fluid flow in a counter-flow direction (at least a component of which is anti-parallel to the principal direction). The counter flow fluid source also acts to restrain the ablation byproducts, so as to ensure that they do not travel too far in the principal direction and that they are not excessively dispersed. The final requirement is a sink, to which fluid moves, which creates a fluid flow oriented in a third direction, at least one component of which is substantially orthogonal to the principal direction. The sink collects the ablation byproducts, removing them from the vicinity of the imaging area.
A third aspect of the invention also concerns a method and apparatus for the removal of byproducts associated with laser ablation on a laser sensitive media. As with the previous embodiments, the first requirement is a principal source of fluid flow, which (a component of which is oriented in a principal direction) directs the ablation byproducts away from the vicinity of the imaging area in the principal direction. A plurality of secondary sources of fluid flow is also provided. They create fluid flow in a secondary direction (at least a component of which is orthogonal to the a surface of the laser sensitive media). The plurality of secondary sources of fluid flow also act to restrain the ablation byproducts, ensuring that they do not travel too far in the principal direction and that they are not excessively dispersed. The method also involves the provision of a sink, to which fluid moves, in a third direction (at least one component of which is substantially orthogonal to the principal direction). The sink collects the ablation byproducts, removing them from the vicinity of the imaging area.
Further advantages of the invention will become apparent when considering the drawings in conjunction with the detailed description.